Silicone rubbers have been widely used in all fields including automobile components such as connector seal and spark plug boots, electric and electronic parts such as rolls in a copying machine and packing in a microwave oven; building materials such as sealant, as well as other products such as feeding bottle nipple and diving gears, in view of the high heat resistance, cold resistance, safety, electric insulation, weatherability, and the like. In these applications, the silicone rubbers are often used in combination with a metal, and also, with an organic resin, and many methods have been proposed to obtain articles wherein an addition curable silicone rubber composition has been integrally cured with a metal or an organic resin. Examples of such typical methods include a method wherein a primer is coated on the surface of the molded resin and an uncured rubber composition is coated over the primer and cured for adhesion; a method wherein an adhesive is coated on the interface for integration of the underlying material and the overlying material; a method wherein two materials are integrated by fitting with each other by double molding; and a method wherein a self-adhesive silicone rubber composition is coated over a molded resin material and cured. However, the methods involving the use of an adhesive or a primer suffered from the problems of increase in the production stages, and also from the problems of contaminating other areas of the surface depending on the method used for the coating. The method using the double molding had constraint in the shape of the integrated article and shortage in the adhesion at the interface. Accordingly, self-adhesive silicone rubber compositions comprising a silicone rubber composition having an adhesive preliminarily added are used, and the use of the self-adhesive silicone rubber composition has become an effective means for producing an article integrally molded with a resin since the coating step as described above is no longer necessary which enabled shorter working time, reduced cost, and improved workability.
Many methods have been proposed for the adhesion of an addition heat curable silicone rubber composition with an organic resin in primer-less molding. An exemplary method is coating of a self-adhesive silicone rubber composition on the resin followed by curing, and various technologies have been proposed for the self-adhesive silicone rubber composition by identifying the adhesive component. Also proposed are a method wherein an organohydrogenpolysiloxane containing at least 30% by mole of hydrogen atoms directly bonded to silicon atoms is added to the organic resin, and this resin is used for the adhesion with an addition-curable silicone rubber composition (Patent Document 1: JP-B H02-34311); a method wherein a silicone rubber composition is adhered to an olefin resin prepared by grafting a compound having an aliphatic unsaturated group and a hydrolyzable group bonded to a silicon atom for the production of an integrated article (Patent Document 2: JP-A S63-183843); and a method wherein a thermoplastic resin having added a compound having an aliphatic unsaturated group and hydrogen atoms bonded to silicon atoms and a silicone rubber composition are adhered for the production of an integrated article, and a method wherein an integral molded article of a resin prepared by blending an oligomer containing an aliphatic unsaturated group to a thermoplastic resin with an oil-bleedable silicone rubber (Patent Document 3: JP-A H09-165516 and Patent Document 4: JP-A H09-165517).
However, in the addition heat curable silicone rubber composition, sufficient adhesion was not obtained by the short time molding when used for the adhesion with general purpose thermoplastic resins such as ABS, PC, PE, PP, PBT, PET, acryl, PA, aromatic PA, PPO, PPS, and urethane, and the resin modification as indicated by the proposals as described above was necessary for a sufficient molding. Such resin modification requires additional step, and hence, increase in the cost, and the resin modification may involve change in the resin properties.
Self-adhesive and addition crosslinkable silicone rubber compositions have been proposed for responding to these problems (Patent Document 5: JP-A H06-172738, Patent Document 6: JP-A 2001-200162, and Patent Document 7: JP-A 2008-537967), and these literatures disclose that the addition of an organohydrogenpolysiloxane having SiH bond and an aromatic skeleton in one molecule in the silicone rubber composition as an adhesion improver material enables adhesion of the silicone rubber composition to an organic resin or a metal even by the short time molding.
However, when the organic resin has a low softening point, the resin deformed under the condition of the curing temperature of typical silicone rubber, namely, at 120 to 220° C., and molding of the resin as designed was sometimes difficult.
In such a case, the molding temperature should be reduced. However, the reduced molding temperature results in the markedly reduced curing speed of the silicone rubber, and hence, longer molding time. When the amount of the curing catalyst is increased to reduce the time required for the molding, pot life and workability are sacrificed.